Estradiol-17β interference with meiotic maturation inRana pipiens ovarian follicles: Evidence for inhibition of 3β-hydroxysteroid dehydrogenase

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Abstract
Increasing doses of estradiol‐17β added to in vitro incubations inhibited pregnenolone‐induced germinal vesicle breakdown in Rana pipiens ovarian follicles. The inhibition was reversed with increasing concentrations of pregnenolone added to the medium. Because no evidence of estradiol‐17β inhibition or interaction with progesterone‐induced GVBD was observed, the effect of estradiol‐17β on the conversion of 3H‐pregnenolone to 3H‐progesterone was investigated. Estradiol‐17β in doses as low as 10−7 M significantly inhibited the conversion of 3H‐pregnenolone to 3H‐progesterone in follicles incubated in vitro. It is suggested that estradiol‐17β is a feedback inhibitor of 3β‐hydroxysteroid dehydrogenase‐isomerase, the enzyme complex that converts pregnenolone to progesterone, a necessary step in the initiation of GVBD.